The present invention relates to microelectronic devices and processing, and more particularly to a microelectronic element and method for forming trench capacitors having different capacitance values on the same microelectronic element.
As the speed and circuit density of integrated circuits (“ICs” or “chips”) is increased from one generation to the next, a greater need exists for capacitive elements that are located close to logic circuits of a chip, or as parts of internal power supply circuits, for example. Thus, capacitive elements must often be provided on the same integrated circuit as such logic circuits and power supply circuits. Trench capacitors are used for storing data bits in some types of dynamic random access memories (DRAMs) and embedded DRAM (eDRAM) macros of chips that contain other functional elements such as processors. In such chips, the use of trench capacitors is favored for other purposes, e.g., to support logic circuits, and as parts of internal power supply circuits, because such other purpose trench capacitors can be formed at the same time as the trench capacitors of the DRAM or eDRAM. When a fairly large amount of capacitance is needed on a chip for such other purpose, a large number of trench capacitors are usually wired together, all having first plates held at a fixed potential such as ground and second plates wired together on which the potential is allowed to vary during operation or remains at a constant potential during operation. In such circumstances, significant usable area of an integrated circuit is occupied by an array of trench capacitors that are wired together of such purpose. Accordingly, the size of such array of trench capacitors is desirably made small, in order not to take up too much of the area of the integrated circuit.
One way of decreasing the size of such capacitor arrays is to enlarge the lateral, i.e. horizontal, dimensions of individual trench capacitors of the array, such as described in U.S. Pat. No. 6,566,191. For example, if the lateral dimension of the trench capacitor of a DRAM array is 90 nm in one lateral direction, the lateral dimension of a trench capacitor used for the different purpose, e.g., to support logic circuits, could be 135 nm, for example. However, the etching of trenches to different lateral dimensions is difficult. Reactive ion etching (RIE) of a hard mask layer and RIE of the underlying semiconductor substrate are difficult to adequately control when trenches having such different dimensions. In particular, the silicon profile control is difficult to maintain during an etching process for simultaneously etching trenches having two different lateral dimensions.
It would be desirable to provide a process of forming trench capacitors in which the lateral dimensions of the trench capacitors are substantially the same, such that the foregoing difficulties in etching are avoided.
In addition to their use for particular purposes on DRAM and logic chips, and combined DRAM and logic chips, capacitive elements are sometimes provided as integrated elements of a passive microelectronic element that contains only passive devices (e.g., capacitors, resistors and/or inductors). Such passive microelectronic element is sometimes referred to as an integrated passives on chip (“IPOC”) element. An IPOC is typically fabricated from a semiconductor, ceramic or glass substrate, having a coefficient of thermal expansion (CTE) that usually matches that of another integrated circuit. The IPOC typically contains a set of contacts on a surface to be bonded to some or all of corresponding contacts of an active chip that has active circuits, e.g., containing elements that have a switching, amplification or rectification function such as transistors and diodes. In such way, the IPOC can be mounted at very close spacing to the other integrated circuit, as through a ball grid array or land grid array, for example. Even in such IPOC, space may need to be conserved, and fabrication techniques may need to be simplified and well-controlled, as it is on an active chip. Accordingly, trench capacitors may be used in such IPOC, in which case, similar considerations apply to their use and fabrication.